The present invention relates to a tagging gas releasing element for detection of a failed fuel, which element is contained in a nuclear fuel rod.
As a method for detecting failed or burst fuels, there is known a so-called tagging method which comprises laballing, or tagging nuclear fuel rods by a tagging gas, sensing leakage of the tagging gas, that is, breakage of a cladding tube of the nuclear fuel rod, by a sensing device disposed in the outside of the fuel rod, and determining a nuclear fuel assembly including the failed fuel rod (see, for example, U.S. patent application Ser. No. 729,317 filed on May 15, 1968).
A prior art method for introducing a tagging gas in a nuclear fuel rod is known in which the tagging gas is sealed in a capsule and, after assembling and sealing the capsule in the nuclear fuel rod, the tagging gas is released and filled in the nuclear fuel rod. For example, according to a method disclosed in French Patent Application No. 7223402, a tagging gas is filled in a capsule composed of a hardly fusible substance, the capsule is arranged within each fuel rod, and the tagging gas is released into the fuel rod through a passage of the capsule intercepted by an easily fusible seal having a melting point lower than the temperature for operating the fuel rod in a nuclear reactor. However, such a prior art tagging gas releasing element is defective in that the manufacture is very difficult because of a complicated structure of the capsule and since the capacity required of the element is large, designing of the nuclear fuel rod is remarkably limited.